The carbon dioxide concentration in the atmosphere has been rising, primarily as a result of fossil fuel burning. The United Nations Framework Convention on Climate Change indicates that there is a need to reduce the CO2 content of the atmosphere for climate and food security reasons.
A natural process by which carbon dioxide in the atmosphere is converted into organic carbon is known. Atmospheric carbon dioxide can dissolve in the ocean and exist in a dissolved or ionic form. This “inorganic carbon” can be converted into “organic carbon” by being taken into the bodies of marine phytoplankton through the process of photosynthesis.
The phytoplankton produced by this conversion eventually perish through age or are eaten by other marine organisms. The resulting dead or excreted biomass then falls to lower levels in the ocean. In this regard, a phenomenon is known whereby organic carbon sinks from the surface ocean to the deep ocean (occurring over most of the ocean) and a compensatory flux of carbon from the deep ocean to the surface occurs by upwelling and diffusion.
Whilst some of the organic carbon material is promptly exported to the deeper ocean, some is converted back into inorganic material in the surface ocean. The recently converted inorganic material can be used by a next generation of phytoplankton to form a new standing stock of organic material. This cycling of carbon in and out of the organic state eventually leads to substantially all of the dissolved inorganic carbon initially converted to organic material being exported from the surface ocean to the deeper ocean.
A process by which photosynthesis in the ocean is caused to increase may assist in decreasing atmospheric carbon dioxide levels by increasing the conversion of inorganic carbon (i.e. dissolved carbon dioxide) to organic carbon (i.e. phytoplankton vegetable matter).
In this respect, the conversion of carbon dioxide dissolved at the surface of the ocean to organic carbon during the sunlit periods is often limited by the availability of specific nutrients, for example, the macronutrient nitrogen or the micronutrient iron. Accordingly, a process of nourishing the ocean can be used to increase the mass of carbon in transit in the deep ocean by providing nutrients that are in short supply to increase photosynthesis and thereby convert a greater amount of inorganic carbon (i.e. dissolved carbon dioxide) to organic carbon.
Methods are known that involve the addition of nutrients such as nitrogen or iron to a body of water in order to increase photosynthesis and cause more carbon dioxide from the atmosphere to dissolve in the ocean. When carbon stored in the deep ocean is supplied by the atmosphere, the process is termed carbon dioxide sequestration. Related sequestration methods in this respect are disclosed in U.S. Pat. No. 5,992,089, and by Jones (1996) in “Enhanced carbon dioxide uptake by the world's ocean” (Energy Convers. & Mgmt, 37, 1049-1052) and Jones and Young (1997) “Engineering a large sustainable world fishery” (Environmental Conservation, 24, 99-104).